Commercialization of Ocean Wave Energy Converters (OWECs) lags significantly behind solar and wind energy even though ocean wave energy is significantly more concentrated, predictable and persistent than the solar energy which produced the winds or the wind energy that produced the ocean waves and swells. Water's high density (over 800 times higher than air) accounts for this high energy density but also increases the challenges of severe sea-state survivability for OWECs. Over 100 OWEC designs have been proposed over the last century yet only a handful of proto-types have only recently been ocean deployed at “commercial scale” (over 150 kw electrical output). No utility scale (over 1 MVV) OWECs have yet been ocean deployed. To make such OWECs survivable in typical 15 meter severe storm waves, most currently proposed OWECs are made of heavy steel plate (like ocean going ships which can survive 15 meter waves). This makes the OWECs both expensive and unresponsive (inefficient) during more normal sea-states. Most OWECs have at least one floating component which moves in response to oncoming waves (i.e., a flop-gate or buoy or float or raft) which is flexibly attached to a second moving or relatively stationary component (a seabed or seawall attachment or a comparable or more massive floating component). As oncoming waves move one component relative to another, a resistive force mechanism absorbs energy (resistive force×distance=energy or work captured).
The “IDEAL OWEC” would be light weight (for high wave responsiveness in all sea conditions), low cost, with high energy capture efficiency in most sea-states, and yet be survivable in severe sea states. It would be deployable in deep water where wave energy levels are highest and potential conflicts with fishing, boating and shoreline visual impacts are minimized. It would be elongated (in the direction parallel to oncoming wave fronts), rather than circular in section, thus intercepting the most wave front energy per unit of OWEC width, area, volume and, therefore, have lower cost/unit width. Circular section and other narrow width buoys, must square their sectional area and cube their volume (exponentially increasing cost) to intercept or access the energy from additional oncoming wave front. Because exactly half of all deep water wave energy is “potential” or “heave” energy (mass of water between the vertical distance between each crest and trough) with the remaining half “kinetic” energy (from the mass of water particle movement), an efficient OWEC must capture most of both wave energy components (or be very inexpensive).
Vertically heaving buoys, can only capture the heave or potential energy component which can never exceed 50% of total wave energy. Near shore deployed floating, bottom pivoting “flap” or “pivoting” or “hinged” gate type OWECs can only capture the kinetic or “surge” energy component of near shore waves which have already lost to bottom friction a major portion of the energy they contained in deep water. Another necessity to high wave energy capture efficiency is to match the wave resistive force of the OWEC to oncoming waves. If the device is too “stiff” or resistive, it will reflect much or most of the impacting wave, partially or totally canceling succeeding oncoming waves, rather than absorbing the wave's energy. If the device's resistive force is too weak, the wave will pass over, under, or through the OWEC rather than being absorbed by it. Because few succeeding waves are alike, an ideal efficient device must sense each successive wave's potential energy and vary the device's resistive force with each wave (or at least adjust to the average wave amplitude and frequency for that time period). If the motion of an OWEC itself produces its own waves, those waves carry away energy not absorbed by the OWEC, and potentially cancel or reduce the energy of oncoming waves. OWECs which have their mass and buoyancy “tuned” to a specific amplitude and period for optimum performance (“resonance” dependent OWECs) with uniform wave produced in a wave test tank have dismal performance in real ocean wave conditions having random amplitudes and periods.